Roundup WeatherMax Research Articles

Influence of Adjuvants on the Efficacy of Tolpyralate plus Atrazine for the Control of Annual Grass and Broadleaf Weeds in Corn with and without Roundup WeatherMAX<sup>®</sup>

Tolpyralate is a new HPPD-inhibiting herbicide that is efficacious on annual grass and broadleaf weed species in corn. For maximum herbicide performance of tolpyralate, it is recommended that atrazine is tank mixed with tolpyralate along with the adjuvants methylated seed oil concentrate (MSO) plus urea ammonia nitrate (UAN). A common use pattern of tolpyralate plus atrazine will be in a tank mix with Roundup WeatherMAX® due to the high proportion of corn acres that are seeded to Roundup Ready® hybrids in Eastern Canada. There is no information in the peer-reviewed literature if the adjuvant system in Roundup WeatherMAX® is adequate for optimal herbicide performance of tolpyralate plus atrazine, or if MSO and UAN are still required. Six field trials were conducted over two years near Ridgetown and Exeter, ON, Canada to determine if adjuvants are still required when tolpyralate plus atrazine is tank mixed with Roundup WeatherMAX® in corn. Tolpyralate plus atrazine plus MSO and Roundup WeatherMAX® plus tolpyralate plus atrazine provided excellent control of velvetleaf, pigweed spp, common ragweed, lambsquarters, ladysthumb, wild mustard, flower-of-an-hour, barnyardgrass and green foxtail in this study. Results of this study show that in the absence of Roundup WeatherMAX®, weed control with tolpyralate plus atrazine was improved substantially with the addition of MSO; however, there was little to no increase in weed control with the addition of UAN. When tolpyralate plus atrazine was co-applied with Roundup WeatherMAX®, there was no improvement in weed control with the addition of MSO and/or UAN.

Influence of Adjuvants on the Control of Glyphosate-Resistant Canada Fleabane and Waterhemp in Corn with Tolpyralate

Tolpyralate is a new benzoylpyrazole herbicide for weed management in corn. It is recommended to be co-applied with atrazine along with the adjuvants methylated seed oil concentrate (MSO) plus an ammonium nitrogen fertilizer, such as urea ammonium nitrate (UAN). Two studies were conducted on glyphosate-resistant (GR) Canada fleabane and GR waterhemp to determine if an additional adjuvant is still required when tolpyralate plus atrazine are tankmixed with a commercial glyphosate formulation (Roundup WeatherMAX®) in corn. Trials were conducted over a two-year period (2018-19) on farms in south western Ontario with confirmed GR populations. When co-applied with Roundup WeatherMAX®, the addition of MSO to tolpyralate + atrazine increased control of GR waterhemp 9%; however, there was no increase in GR Canada fleabane control from the addition of additional adjuvants. At 8 WAA, all treatments provided > 91% and > 84% control of GR waterhemp and GR Canada fleabane, respectively. This study concludes that the addition of Roundup WeatherMAX® to tolpyralate plus atrazine improves the control of GR waterhemp and GR Canada fleabane in corn.

Comparison of WeatherMax<sup>®</sup> and Engame<sup>TM</sup> Formulations of Glyphosate on Cotyledon Surface Structure, Chlorophyll A Fluorescence and Shikimate Levels in Isogenic Cotton Cultivars Differing in Roundup Resistance

The effects of Roundup WeatherMax® and EngameTM formulations of glyphosate were investigated on the cotyledons of glyphosate resistant (GR) and glyphosate sensitive (GS) isogenic cotton cultivars. EngameTM is a mixture of glyphosate and 1-aminomethanamide dihydrogen tetraoxosulfate (AMADS). Fully expanded cotton cotyledons treated with EngameTM or AMADS developed surface lesions within 2 hours after treatment whereas surfactant-treated control or WeatherMax®-treated tissues did not develop lesions. The EngameTM and AMADS damage appeared as depressions which were confirmed by scanning electron microscopy. Light micrographs of cross sections through the depressions revealed collapsed and compressed epidermal and mesophyll cells with congealed cytoplasmic contents in the palisade and spongy mesophyll cells. Changes to photosynthetic electron transport were evident at 4 hours after treatment (HAT) in all treatments as revealed by chlorophyll A fluorescence. In GR cotton, the fluorescence perturbations decreased with time such that at 72 HAT EngameTM-treated cotyledons could not be distinguished from the surfactant-or WeatherMax®-treated plants. The GS cotton continued to show progressive decreases in the fluorescence parameters Fv/Fm and performance index (PI) to 72 HAT. Shikimate levels increased following glyphosate treatment in glyphosate sensitive cotton and EngameTM caused a two-to three-fold greater increase in shikimate compared to WeatherMax®. These results indicate that the EngameTM-based glyphosate formulation involved structural tissue damage which likely increased glyphosate uptake and subsequently increased inhibition of photosynthesis and the shikimate pathway.

Wheat preharvest herbicide application, whole‐grain flour properties, yeast activity and the degradation of glyphosate in bread

SummaryThe aim of this study was to determine the effects of wheat preharvest application of a glyphosate‐based herbicide (Roundup WeatherMax® with Transorb® 2 Technology) on whole‐grain flour composition and properties, including yeast activity. The effect of dough fermentation on the degradation of herbicide residues was also estimated. Grain samples from two hard red spring wheat varieties exceeded the maximum residue limits (5 mg kg−1) in Canada. Glyphosate had minor effects on wheat kernels composition and properties, including fructans content and yeast gassing power. No degradation of Roundup® or pure glyphosate was seen after dough fermentation for up to 4 h and baking. These results call for more scientific studies on glyphosate residues in wheat.

The combined influence of two agricultural contaminants on natural communities of phytoplankton and zooplankton.

Concentrations of glyphosate observed in the environment are generally lower than those found to exert toxicity on aquatic organisms in the laboratory. Toxicity is often tested in the absence of other expected co-occurring contaminants. By examining changes in the phytoplankton and zooplankton communities of shallow, partitioned wetlands over a 5month period, we assessed the potential for direct and indirect effects of the glyphosate-based herbicide, Roundup WeatherMax(©) applied at the maximum label rate, both in isolation and in a mixture with nutrients (from fertilizers). The co-application of herbicide and nutrients resulted in an immediate but transient decline in dietary quality of phytoplankton (8.3% decline in edible carbon content/L) and zooplankton community similarity (27% decline in similarity and loss of three taxa), whereas these effects were not evident in wetlands treated only with the herbicide. Thus, even at a worst-case exposure, this herbicide in isolation, did not produce the acutely toxic effects on plankton communities suggested by laboratory or mesocosm studies. Indirect effects of the herbicide-nutrient mixture were evident in mid-summer, when glyphosate residues were no longer detectable in surface water. Zooplankton abundance tripled, and zooplankton taxa richness increased by an average of four taxa in the herbicide and nutrient treated wetlands. The lack of significant toxicity of Roundup WeatherMax alone, as well as the observation of delayed interactive or indirect effects of the mixture of herbicide and nutrients attest to the value of manipulative field experiments as part of a comprehensive, tiered approach to risk assessments in ecotoxicology.

Variation in amphibian response to two formulations of glyphosate-based herbicides.

Variation in toxicity among formulations and species makes it difficult to extrapolate results to all species and all formulations of herbicides. The authors exposed larval wood frogs (Lithobates sylvaticus) from 4 populations to 2 glyphosate-based herbicides, Roundup Weed and Grass Control® and Roundup WeatherMax®. The 96-h median lethal concentration values for both formulations varied among the populations (Roundup Weed and Grass Control, 0.14 mg acid equivalents (a.e.)/L to 1.10 mg a.e./L; Roundup WeatherMax, 4.94 mg a.e./L to 8.26 mg a.e./L), demonstrating that toxicity varies among the formulations and that susceptibility may differ among populations.

Role of sediments in modifying the toxicity of two Roundup formulations to six species of larval anurans.

The role of sediment in modifying the toxicity of the original formulation of Roundup® and Roundup WeatherMAX® was examined in aqueous laboratory tests. Six species of anurans (Bufo fowleri, Hyla chrysoscelis, Rana catesbeiana, Rana clamitans, Rana sphenocephala, and Rana pipiens) were exposed at Gosner stage 25 to concentrations of the 2 herbicide formulations in 96-h, static, nonrenewal experiments in the presence and absence of sediment. All species tested had lower median lethal concentration values in water-only exposures of both formulations compared with exposures with sediment. Sediment significantly altered the potency slopes in all tests with the exceptions of H. chrysoscelis and R. clamitans when exposed to the original formulation of Roundup and H. chrysoscelis and R. sphenocephala when exposed to Roundup WeatherMAX. Thresholds were significantly different in all tests, including those in which potency slopes did not differ. Based on water-sediment exposures of the original formulation of Roundup, all 6 species tested had a margin of safety when compared with the predicted environmental concentration of the highest label application rate. Of the 6 species, 5 had a margin of safety when exposed to Roundup WeatherMAX. During incidental exposures in the field, sediments and organic matter present in aquatic systems provide significant sources of environmental ligands. If used according to label instructions, both herbicides should pose minimal risk to anuran amphibians in actual field applications. Environ Toxicol Chem 2014;33:2616-2620. © 2014 SETAC.

The response of amphibian larvae to exposure to a glyphosate-based herbicide (Roundup WeatherMax) and nutrient enrichment in an ecosystem experiment

Herbicides and fertilizers are widely used throughout the world and pose a threat to aquatic ecosystems. Using a replicated, whole ecosystem experiment in which 24 small wetlands were split in half with an impermeable barrier we tested whether exposure to a glyphosate-based herbicide, Roundup WeatherMax™, alone or in combination with nutrient enrichment has an effect on the survival, growth or development of amphibians. The herbicide was applied at one of two concentrations (low=210μga.e./L, high=2880μga.e./L) alone and in combination with nutrient enrichment to one side of wetlands and the other was left as an untreated control. Each treatment was replicated with six wetlands, and the experiment was repeated over two years. In the high glyphosate and nutrient enrichment treatment the survival of wood frog (Lithobates sylvaticus) larvae was lower in enclosures placed in situ on the treated sides than the control sides of wetlands. However, these results were not replicated in the second year of study and they were not observed in free swimming wood frog larvae in the wetlands. In all treatments, wood frog larvae on the treated sides of wetlands were slightly larger (<10%) than those on the control side, but no effect on development was observed. The most dramatic finding was that the abundance of green frog larvae (Lithobates clamitans) was higher on the treated sides than the control sides of wetlands in the herbicide and nutrient treatments during the second year of the study. The results observed in this field study indicate that caution is necessary when extrapolating results from artificial systems to predict effects in natural systems. In this experiment, the lack of toxicity to amphibian larvae was probably due to the fact the pH of the wetlands was relatively low and the presence of sediments and organic surfaces which would have mitigated the exposure duration.

The direct and indirect effects of a glyphosate-based herbicide and nutrients on Chironomidae (Diptera) emerging from small wetlands.

Laboratory and mesocosm experiments have demonstrated that some glyphosate-based herbicides can have negative effects on benthic invertebrate species. Although these herbicides are among the most widely used in agriculture, there have been few multiple-stressor, natural system-based investigations of the impacts of glyphosate-based herbicides in combination with fertilizers on the emergence patterns of chironomids from wetlands. Using a replicated, split-wetland experiment, the authors examined the effects of 2 nominal concentrations (2.88 mg acid equivalents/L and 0.21 mg acid equivalents/L) of the glyphosate herbicide Roundup WeatherMax, alone or in combination with nutrient additions, on the emergence of Chironomidae (Diptera) before and after herbicide-induced damage to macrophytes. There were no direct effects of treatment on the structure of the Chironomidae community or on the overall emergence rates. However, after macrophyte cover declined as a result of herbicide application, there were statistically significant increases in emergence in all but the highest herbicide treatment, which had also received no nutrients. There was a negative relationship between chironomid abundance and macrophyte cover on the treated sides of wetlands. Fertilizer application did not appear to compound the effects of the herbicide treatments. Although direct toxicity of Roundup WeatherMax was not apparent, the authors observed longer-term impacts, suggesting that the indirect effects of this herbicide deserve more consideration when assessing the ecological risk of using herbicides in proximity to wetlands.

Effects of glyphosate-based herbicides on survival, development, growth and sex ratios of wood frog (Lithobates sylvaticus) tadpoles. II: Agriculturally relevant exposures to Roundup WeatherMax® and Vision® under laboratory conditions

Glyphosate-based herbicides are currently the most commonly used herbicides in the world. They have been shown to affect survival, growth, development and sexual differentiation of tadpoles under chronic laboratory exposures but this has not been investigated under more environmentally realistic conditions. The purpose of this study is (1) to determine if an agriculturally relevant exposure to Roundup WeatherMax®, a relatively new and understudied formulation, influences the development of wood frog tadpoles (Lithobates sylvaticus) through effects on the mRNA levels of genes involved in the control of metamorphosis; (2) to compare results to the well-studied Vision® formulation (containing the isopropylamine salt of glyphosate [IPA] and polyethoxylated tallowamine [POEA] surfactant) and to determine which ingredient(s) in the formulations are responsible for potential effects on development; and (3) to compare results to recent field studies that used a similar experimental design. In the present laboratory study, wood frog tadpoles were exposed to an agriculturally relevant application (i.e., two pulses) of Roundup WeatherMax® and Vision® herbicides as well as the active ingredient (IPA) and the POEA surfactant of Vision®. Survival, development, growth, sex ratios and mRNA levels of genes involved in tadpole metamorphosis were measured. Results show that Roundup WeatherMax® (2.89mg acid equivalent (a.e.)/L) caused 100% mortality after the first pulse. Tadpoles treated with a lower concentration of Roundup WeatherMax® (0.21mg a.e./L) as well as Vision® (2.89mg a.e./L), IPA and POEA had an increased condition factor (based on length and weight measures in the tadpoles) relative to controls at Gosner stage (Gs) 36/38. At Gs42, tadpoles treated with IPA and POEA had a decreased condition factor. Also at Gs42, the effect on condition factor was dependent on the sex of tadpoles and significant treatment effects were only detected in males. In most cases, treatment reduced the normal mRNA increase of key genes controlling development in tadpoles between Gs37 and Gs42, such as genes encoding thyroid hormone receptor beta in brain, glucocorticoid receptor in tail and deiodinase enzyme in brain and tail. We conclude that glyphosate-based herbicides have the potential to alter mRNA profiles during metamorphosis. However, studies in natural systems have yet to replicate these negative effects, which highlight the need for more ecologically relevant studies for risk assessment.

Glyphosate-based herbicides on weeds management and maize performance under conservation agriculture practices in eastern Kenya

A three-season research study was conducted at Embu Agricultural Research Station farm to determine the effect of glyphosate-based herbicides on weeds management and maize (Zea mays L.) performance under zero-tillage conservation agriculture practice. Glyphosate herbicide sprays were prepared from Roundup Turbo product at the rate of 2.5 L ha–1 and Roundup Weathermax at 1.5, 2.5 and 3.0 L ha–1 rates. Significant (p ≤ 0.05) differences in weeds management were observed under the tested rate of Roundup Turbo compared to un-weeded control plots. The average grain yield from conventionally tilled plots was 3.6 t ha–1. This did not differ significantly from those of herbicide-managed plots. Low-grain yield (0.1 t ha–1) was observed from un-weeded plots compared to those from zero-tilled plots that had also exhibited significantly (p ≤ 0.05) higher net-benefits. The study concluded that the application of herbicides improves weeds control and maize performance.

Comparison of Glyphosate Formulations for Weed Control and Tolerance in Maize (&amp;lt;i&amp;gt;Zea mays&amp;lt;/i&amp;gt; L.) and Soybean [&amp;lt;i&amp;gt;Glycine max&amp;lt;/i&amp;gt; (L.) Merr.

Twenty-two field experiments (six maize (Zea mays L.) and five soybean [Glycine max (L.) Merr.] using low glyphosate doses to assess weed control and six maize and five soybean using high glyphosate doses to assess tolerance) were conducted from 2010 to 2012 at two locations in southern Ontario, Canada to compare the commercially available glyphosate formulations of Roundup Weather MAX?, Clearout?41 Plus, and Wise Up? (WeatherMAX, Clearout, and WiseUp, respectively). Inmaize and soybean, control of velvetleaf, pigweed species, common lambs quarters, and green foxtail 4 weeks after treatment (WAT) using 900 g·ae·ha-1 ranged from at least 85% to 99%, regardless of formulation. By 8 WAT with 900 g·ae·ha-1, control of these weeds generally declined, but still ranged from 82% to 97% across all formulations. At harvest, maize yields were similar to the weed-free control for 900 g·ae·ha-1 of glyphosate as WeatherMAX and Clearout; however, reduced weed control with WiseUp resulted in an 8.8% yield loss. For soybean, yields were similar to the weed-free control, regardless of formulation or dose. In the tolerance experiments, 2.1% and 2.8% injury was observed 4 WAT for maize treated with 3600 g·ae·ha-1 of glyphosate as WeatherMAX and WiseUp, respectively. However, maize yields were unaffected by glyphosate formulation or dose. In soybean, visible injury of 8.5%, 4.5%, and 3.7% was observed 1 WAT with 5400 g·ae·ha-1 of glyphosate as WeatherMAX, WiseUp, and Clearout, respectively; by 8 WAT, visible injury was similar to the untreated control, regardless of formulation or dose. The early injury from 5400 g·ae·ha-1 of glyphosate resulted in 8.5%, 4.6%, and 5.5% yield loss for the WeatherMAX, WiseUp, and Clearout formulations, respectively.

Effects of the glyphosate-based herbicide Roundup WeatherMax® on metamorphosis of wood frogs (Lithobates sylvaticus) in natural wetlands

Amphibian tadpoles develop in aquatic environments where they are susceptible to the effects of pesticides and other environmental contaminants. Glyphosate-based herbicides are currently the most commonly used herbicide in the world and have been shown to affect survival and development of tadpoles under laboratory and mesocosm conditions. In the present study, whole wetland manipulations were used to determine if exposure to an agriculturally relevant application of Roundup WeatherMax®, a herbicide formulation containing the potassium salt of glyphosate and an undisclosed surfactant, influences the development of wood frog tadpoles (Lithobates sylvaticus) under natural conditions. Wetlands were divided in half with an impermeable curtain so that each wetland contained a treatment and control side. Tadpoles were exposed to two pulses of this herbicide at an environmentally realistic concentration (ERC, 0.21mg acid equivalent (a.e.)/L) and the predicted maximum environmental concentration (PMEC, 2.89mg a.e./L), after which abundance, growth, development, and mRNA levels of genes involved in tadpole metamorphosis were measured. Results present little evidence that exposure to this herbicide affects abundance, growth and development of wood frog tadpoles. As part of the Long-term Experimental Wetlands Area (LEWA) project, this research demonstrates that typical agricultural use of Roundup WeatherMax® poses minimal risk to larval amphibian development. However, our gene expression data (mRNA levels) suggests that glyphosate-based herbicides have the potential to alter hormonal pathways during tadpole development.

Laboratory and field exposure of two species of juvenile amphibians to a glyphosate-based herbicide and Batrachochytrium dendrobatidis

Herbicides are commonly used in agriculture and silviculture to reduce interspecific competition among plants and thereby enhance crop growth, quality, and volume. Internationally, formulations of glyphosate-based herbicides are the most widely used herbicides in both these sectors. A large amount of work has focused on the effects of these herbicides on amphibians. Several laboratory and mesocosm studies have demonstrated that various formulations of glyphosate herbicides can be acutely toxic to larval and juvenile amphibians at concentrations at the upper end of environmental realism. However, to date there has been little work done investigating such effects in natural systems, limited work on juvenile amphibians, and only a few studies have investigated interactions with other stressors. We conducted a 16day field experiment in which juveniles of two amphibian species (Lithobates clamitans and Lithobates pipiens) were exposed to the herbicide Roundup WeatherMax™ at four application rates (0, 2.16, 4.32 and 8.64kg a.e./ha) to investigate effects on survival, liver somatic index (LSI), body condition, and incidence of disease caused by Batrachochytrium dendrobatidis (Bd). In a separate 16day laboratory experiment, we exposed juvenile L. clamitans to both the herbicide and Bd. Results of our studies showed that this particular herbicide formulation had no effect on juvenile survival, LSI, body condition, or disease incidence, nor was there an interaction between exposure to herbicide and exposure to the disease in tests which closely mimic real world exposure scenarios. These experiments suggest that Roundup WeatherMax as typically used in agriculture is unlikely to cause significant deleterious effects on juvenile amphibians under real world exposure conditions.

Review of the Séralini et al. (2012) publication on a 2‐year rodent feeding study with glyphosate formulations and GM maize NK603 as published online on 19 September 2012 in Food and Chemical Toxicology

On 19 September 2012, Séralini et al. published online in the scientific journal Food and Chemical Toxicology a publication describing a 2-year feeding study in rats investigating the health effects of genetically modified (GM) maize NK603 with and without Roundup WeatherMAX® and Roundup® GT Plus alone (both are glyphosate-containing plant protection products). EFSA was requested by the European Commission to review this publication and to identify whether clarifications are needed from the authors. EFSA notes that the Séralini et al. (2012) study has unclear objectives and is inadequately reported in the publication, with many key details of the design, conduct and analysis being omitted. Without such details it is impossible to give weight to the results. Conclusions cannot be drawn on the difference in tumour incidence between the treatment groups on the basis of the design, the analysis and the results as reported in the Séralini et al. (2012) publication. In particular, Séralini et al. (2012) draw conclusions on the incidence of tumours based on 10 rats per treatment per sex which is an insufficient number of animals to distinguish between specific treatment effects and chance occurrences of tumours in rats. Considering that the study as reported in the Séralini et al. (2012) publication is of inadequate design, analysis and reporting, EFSA finds that it is of insufficient scientific quality for safety assessment. Therefore EFSA, concludes that the Séralini et al. study as reported in the 2012 publication does not impact the ongoing re-evaluation of glyphosate, and does not see a need to reopen the existing safety evaluation of maize NK603 and its related stacks. EFSA will give the authors of the Séralini et al. (2012) publication the opportunity to provide further information on their study to EFSA.

Assessing Crop Injury Caused by Aerially Applied Glyphosate Drift Using Spray Sampling

Crop injury caused by off-target drift of aerially applied glyphosate is of great concern to farmers and aerial applicators. An experiment was conducted in 2009 to determine the extent of injury due to near-field glyphosate drift from aerial application to glyphosate-sensitive cotton, corn, and soybean. The drift effects on different crops were characterized in a field planted in alternating blocks of these sensitive crops. Spray samplers were placed in the spray swath and downwind to quantify relative concentrations of the applied chemical. An Air Tractor 402B spray airplane equipped with fifty-four CP-09 nozzles was flown down the center of the field, applying 866 g a.e. ha-1 glyphosate (Roundup Weathermax) and rubidium chloride tracer at a 2.6 g ha-1 spray rate. Relative concentrations of the tracer were quantified from downwind spray samplers by atomic absorption spectroscopy. Biological responses of the crops to the glyphosate drift were measured at weekly intervals, along with airborne multispectral imaging. Statistical analysis indicated that spray drift sampling was able to explain downwind crop injury, and physical responses could be estimated for evaluating crop injury caused by the drift of aerially applied glyphosate. Correlations between the relative concentration of the spray tracer and the crop biological responses identified that cotton was less sensitive to glyphosate drift than corn and soybean. Regression models for the injuries of cotton and soybean one and two weeks after field treatment and for the injury of corn one week after treatment with the percent applied glyphosate from the label rate were developed and evaluated with chlorophyll data. The cotton models for visual injury and plant height at one and two weeks after treatment were well validated with chlorophyll data (average of 1 for the ratio of estimated vs. measured chlorophyll, and low root mean squared deviations). However, in validation of the corn model, the ratio of estimated vs. measured chlorophyll deviated from 1. Compared with validation of the corn model, the validation of the soybean models showed less bias, with a value close to 1 for the ratio of estimated vs. measured chlorophyll. These results have established a method of characterizing crop injury caused by aerially applied glyphosate and can provide guideline data for use by farmers and aerial applicators.

Comparative toxicity of two glyphosate formulations (original formulation of Roundup® and Roundup WeatherMAX®) to six North American larval anurans

The toxicity of two glyphosate formulations (the original formulation of Roundup® and Roundup WeatherMAX®) to six species of North American larval anurans was evaluated by using 96-h static, nonrenewal aqueous exposures. The 96-h median lethal concentration values (LC50) ranged from 1.80 to 4.22 mg acid equivalent (ae)/L and 1.96 to 3.26 mg ae/L for the original formulation of Roundup and Roundup WeatherMAX, respectively. Judged by LC50 values, four species were more sensitive to Roundup WeatherMAX exposures, and two species were more sensitive to the original formulation. Two of six species, Bufo fowleri (p < 0.05, F = 14.89, degrees of freedom [df] = 1) and Rana clamitans (p < 0.05, F = 18.46, df = 1), had significantly different responses to the two formulations tested. Increased sensitivity to Roundup WeatherMAX likely was due to differences in the surfactants or relative amounts of the surfactants in the two formulations. Potency slopes for exposures of the original formulation ranged from 24.3 to 92.5% mortality/mg ae/L. Thresholds ranged from 1.31 to 3.68 mg ae/L, showing an approximately three times difference in the initiation of response among species tested. For exposures of Roundup WeatherMAX, slopes ranged from 49.3 to 84.2% mortality/mg ae/L. Thresholds ranged from 0.83 to 2.68 mg ae/L. Margins of safety derived from a simulated direct overspray were above 1, except for one species in exposures of Roundup WeatherMAX. Laboratory data based on aqueous exposures are conservative because of the lack of environmental ligands; however, these tests provide information regarding the relative toxicity between these two Roundup formulations.

Acute and chronic toxicity of Roundup Weathermax ® and Ignite ® 280 SL to larval Spea multiplicata and S. bombifrons from the Southern High Plains, USA

Pesticides have been implicated in widespread amphibian declines. We assessed acute and chronic toxicity of two widely used herbicides to larval New Mexico ( Spea multiplicata) and Plains ( S. bombifrons) spadefoots from cropland and native grassland playas. Roundup WeatherMAX ® (WM) toxicity estimates (48- and 216-h LC 50; 48-h LC 1) for both species were similar to environmental concentrations expected from accidental overspray. Chronic (30-day) exposure to WM at predicted environmental concentrations (2.0 and 2.8 mg glyphosate acid equivalents/L) reduced survival of both species. Ignite ® 280 SL (IG) toxicity estimates (48-h LC 50 and LC 1) for both species were above predicted environmental concentrations of 1.0 mg glufosinate/L. Chronic exposure to predicted environmental concentrations of IG did not reduce survival of either species. Toxicity test results suggest that at predicted environmental concentrations IG would not cause extensive mortalities among larval New Mexico and Plains spadefoots. However, WM may cause extensive mortality among larvae of these species.

Larval Responses of Three Midwestern Anurans to Chronic, Low-Dose Exposures of Four Herbicides

Low levels of agricultural herbicides often contaminate surface water and might persist throughout the growing season, potentially acting as stressors on aquatic organisms. Although low-dose, chronic exposures to agrochemicals are likely common for many nontarget organisms, studies addressing these effects using end-use herbicide formulations are rare. We exposed three common species of tadpoles to conservative levels of atrazine, S-metolachlor, and glyphosate end-use herbicide formulations throughout the larval period to test for survival differences or life-history trait alterations. Exposure to the glyphosate product Roundup WeatherMax at 572 ppb glyphosate acid equivalents (a.e.) resulted in 80% mortality of western chorus frog tadpoles, likely as a result of a unique surfactant formulation. Exposure to WeatherMax or Roundup Original Max at 572 ppb a.e. also lengthened the larval period for American toads. Chronic atrazine and S-metolachlor exposures induced no significant negative effects on survival, mass at metamorphosis, or larval period length at the levels tested. These results highlight the importance of explicitly tying chronic tests to the natural environment and considering contributions of surfactant/adjuvant components to end-use formulation toxicities, even between very similar products.

Aphid Transmission of Banana Bunchy Top Virus to Bananas After Treatment With a Bananacide

Field and laboratory studies were conducted to determine the impact of using a herbicide as a bananacide on aphid transmission of Banana bunchy top virus (family Nanoviridae, genus Babuvirus, BBTV) to healthy banana (Musa spp.) plants. BBTV-infected banana plants in a commercial orchard were treated with Roundup Weathermax herbicide. Using polymerase chain reaction, the time after herbicide treatment that BBTV could no longer be detected in the infected plants was determined. The impact of the herbicide treatment on Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae) virus acquisition and ability to inoculate healthy banana plants with BBTV also were determined. Generally, banana plants were dead beyond 42 d after herbicide injection (DAI), and BBTV was detected in a similar high percentage of treated plants from 0 up to 21 DAI. During two field trials, 0 and 32% of P. nigronervosa acquired the virus from treated plants at 42 DAI, respectively, but none successfully inoculated a healthy banana plant beyond 35 DAI. Finally, 22% of P. nigronervosa colonies collected directly from the pseudostem of injected plants at the final sample date (42 DAI) tested positive for BBTV and infected 9.5% of the healthy banana plants. The findings indicate that banana plants may remain a potential source of virus inoculum 6 wk after injection with a bananacide. The implications of these findings with respect to BBTV management are discussed.